Polyacrylamide gel electrophoresis (PAGE) is a technique widely used to separate biological molecules, for example, proteins, by their size, hence, mobility in an electric field. When sodium dodecyl sulfate (SDS) is used to denature the proteins and the polyacrylamide gel is used as a support medium, this method is referred to as SDS-PAGE. A typical set-up of SDS-PAGE is illustrated in FIG. 1.
Protein separation by SDS-PAGE may be used to estimate relative molecular weight (MW) of an unknown protein or determine relative abundance of proteins in a sample. The relationship between mobility (x, the relative distance travelled in a given amount of time) and molecular weight (MW) may be represented by a linear or nearly linear equation of:Log MW=−mx+b  (Equation 1)where m is the slope and b is the Log MW-intercept.
Preparation of SDS-PAGE requires casting two layers of acrylamide gel between glass plates 102. As seen in the schematic diagram 100 of FIG. 1, the bottom layer, also known as a separation gel 104 is responsible for separating proteins by size, while the top layer, known as a stacking gel 106 includes sample wells 108. A positive electrode 110 of an electrical source (not shown in FIG. 1) is placed toward one end of the acrylamide gel that is at the separation gel 104, while a negative electrode 112 of the electrical source is placed toward the opposite end of the acrylamide gel that is near the sample wells 108 at the stacking gel 106. A moving boundary sweeps proteins 114, 116 in a sample, compressing (stacking) these proteins 114, 116 into thin layers (for example, micrometer thin layers) at the stacking gel 106 before these proteins 114, 116 reach the separation gel 104. When the electrical field is applied across the positive electrode 110 and the negative electrode 112 over the two layers 104, 106 in a buffer solution 118, the proteins 114, 116 move into the separation gel 104 with the smaller proteins 114 moving faster and the larger proteins 116 moving slower toward the positive electrode 110.
Manual gel casting for SDS-PAGE is time-consuming (usually more than 3 hours) and often leads to inconsistent results. For example, common problems due to inappropriate operation of manual gel casting may include unevenly poured acrylamide mixture resulting in smeared gel, light bands from poorly formed wells during gel casting, and others. Moreover, a number of reagents used for gel casting may be toxic. For instance, the main component of acrylamide is a potent neurotoxin and requires careful handling.
Another problem with conventional SDS-PAGE is that it usually requires large amount of expensive reagents in each test due to the size of gel casting jig and gel electrophoresis tank. On the other hand, use of commercially available precast gels may be able to reduce the researchers' invested time and to some extent, minimize the problems of manual preparation of gel. However, such precast gels are generally more expensive when compared to manual gel casting, and this may impact a laboratory's budget and running cost.
Thus, there is a need for a gel electrophoresis device that is cost effective, ready-to-use and user-friendly to address at least the problems above.